The present invention relates to fluid flow machines in general, especially to improvements in centrifugal pumps. More specifically, the invention relates to improvements in radial impellers.
It is well known that specific speed is a frequently utilized characteristic of the optimal impeller shape required to achieve optimum efficiency of a fluid flow machine. For a radial impeller, the specific speed (nq) is normally between 11 and 35 min.sup.-1. It is also known that the specific speed of a radial impeller can be varied by changing the outer diameters of its coverplates. Such changes of nq will be needed when the designer wishes to change the efficiency of the machine wherein the impeller is installed.
AT-PS No. 1 22 689 discloses that the operation of centrifugal pumps can be caused to conform to varying conditions by hollowing out the vanes of the impeller or by changing the outer diameter of the impeller. A drawback of such proposal is that each of these steps invariably entails a change in total head (H) as well as a change in the capacity (Q) of the machine.